1. Field of the Invention
The present invention relates to a new fin pattern of a ribbed vortex generator. Especially, the present invention relates to a new fin pattern of a ribbed vortex generator that applies most often in air conditioners and air-cooling heat exchangers to generate turbulence and to improve heat transfer.
2. Description of the Prior Art
In recent years, the application of vortex generators in heat exchangers has received much attention. In order to increase overall performance of heat transfer, many improvements on the application of enhanced surface have been developed. In the article by M. Fibig in 1998 xe2x80x9cVortices, generators and heat transfer, Trans.IchemExe2x80x9d, there are three major improvements of surface application to enhance the performance of heat transfer, namely (1) developing boundary layer, (2) swirl or vortices, (3) flow destabilization or turbulence intensification. In 2000, Dr. Chi-Chun Wang in his article xe2x80x9cTechnology reviewxe2x80x94a survey of the recent progress of the patents of fin-and-tube Heat Exchanges, J. of Enhanced Heat Transferxe2x80x9d mentioned that the most common surface improvements in heat transfer are interrupted surfaces, as slits, offset strips, and louvers. The interrupted surface technology improves the performance of heat transfer extremely; however, the associated penalty of pressure drop is also tremendous. Comparing with interrupted surface technology, vortex generators not only keep the advantage of the three major mechanisms but also reveals comparatively small pressure drops. That is because the friction on surface is related to spanwise and normal velocities instead of streamwise velocity. The vortex generators characterized the secondary flow pattern from the vertical motion is caused by the spanwise and normal velocities. Heat transfer enhancement is associated with the secondary flow but with a lower penalty of friction. Therefore, longitudinal vortices are recognized especially suitable for heat transfer applications.
The article related to the improvement of heat transfer is seen earliest in xe2x80x9cThe improvement of forced convection surface heat transfer using surface protrusions in the form of (A) cubes and (B) vortex generators.xe2x80x9d by Edwards and Alker in 1974. In the article, it mentioned that the coefficient of partial heat transfer could be higher than that of plane fin surface by 40%.
Therefore, to increase the performance of the flow destabilization and the turbulence intensification will also increase the performance of air flow mixing. The problem of how to increase the performance of the flow destabilization and the turbulence intensification to obtain the best heat transfer performance, but still keep the pressure drop to the minimum level, is a critical issue in surface application. Meanwhile, the improvement of the shape of a vortex generator is an important topic in development.
The inventor of the present invention is identical to the inventor in ROC patent 446109. In the case of ROC patent 446109, some curve-shaped protruding turbulent cubes are placed around the heat transfer fin to enhance the heat transfer performance. According to the test, there is much improvement therewith.
The present invention relates to a new fin pattern of a ribbed vortex generator which includes non-equal-height rib-shaped prism-like structure (prisms) placed on fin of a vortex generator. When the fluid flows thru heat exchanger, the prisms of the vortex generator will create vortices to enhance the performance of the flow destabilization and the turbulence intensification but with much less pressure drop and further mix the fluid flowing to obtain the best heat transfer performance.
In order to achieve the purpose described above, in one embodiment of the present invention, there are multiple prisms placed around the round tube of the vortex generator. The height of two ends of the prism is not equal, which means one end is higher and another end is lower. The prisms are placed around the round tube on the fin of the vortex generator concentric with the center of the round tube. A first pair of the prisms forms a fluid entry and a second pair of the prisms forms a fluid exit. The fluid will be led into the entry formed by a higher end of the first pair of prisms, flow along the path formed by the round tube and the vortex generator, and leave from the exit formed by the higher end of the second pair of prisms. So, the disturbing performance is enhanced during the fluid flowing, and the heat around the back end of the round tube will be brought away as well, however, the pressure drop is relatively much less. Additionally, vortices will be created when fluid flows thru the path, which causes more extra air be drawn into the area of the fin of the heat exchanger and further improves the performance of heat transfer.